Watch for annual fees. For example, I think Southwest is $59. Some airlines offer no fee for the first 1 or 2 years, some offer bonus miles/credits to start. I got a SW card last April at the stand in the airport, I got 8 bonus credits, which combined with what I had in my account gave me a free ticket for December. It's coming up for renewal and I'm going to cancel it rather than pay the $59 fee again (you only get the bonus at sign-up). If you are looking at a card with an airline that uses miles, keep in mind that it can be very difficult to get a 25,000 mile award ticket.